> On Tue, Dec 15, 2020 at 9:57 AM Mark Polesky via Python-list <
> python-list@python.org> wrote:
>
>> Hi.
>>
>> # Running this script....
>>
>> D = {'a':1}
>> def get_default():
>> print('Nobody expects this')
>> return 0
>> print(D.get('a', get_default()))
>>
>> # ...generates this output:
>>
>> Nobody expects this
>> 1
>>
>> ###
>>
>> Since I'm brand new to this community, I thought I'd ask here
first... Is
>> this worthy of a bug report? This behavior is definitely unexpected
to me,
>> and I accidentally coded an endless loop in a mutual recursion situation
>> because of it. Calling dict.get.__doc__ only gives this short sentence:
>> Return the value for key if key is in the dictionary, else default.
>> Nothing in that docstring suggests that the default value is
evaluated even
>> if the key exists, and I can't think of any good reason to do so.
Hey this is fun! A quick search reveals that I've (mea culpa) always
thought of dict.get() as providing a default *value* and not used a
function in there to provide said value.
That said, the function's name says it all: get_default(). Is it
'getting' a default value? No, it's (also) reporting-back. Thus a
"side-effect". Undesirable, as you say.
Were it appropriate to report that a default value was necessary, maybe
something like:
try:
print( d[ 'a' ] )
except KeyError:
print( "Nobody expects this" )
d[ 'a' ] = 0
--
Regards =dn
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